Molecular electronics generally and molecular switches, in particular, have been subjects of interest. One molecular switch that has been studied includes a rotaxane molecule and a catenane molecule. The rotaxane molecule includes an “axle” having a long, straight molecule and one or more rings. The rings are threaded onto the axle and bulky groups are bonded onto the end of the axle. This structure has been described as preventing the rings from sliding off without having any chemical bonds between the ring and the axle. The catenane molecule includes two interlocking rings. In one molecular switch, the catenane molecule is trapped between two metal electrodes and is switched from an ON state to an OFF state by the application of a positive bias across the molecule. The ON and OFF states differ in resistivity by about a factor of 100 and 5, respectively, for the rotaxane molecule and catenane molecule.
The rotaxane-based switch is an irreversible switch. It can only be toggled once. Thus, it could be used in a programmable read-only memory (PROM), but not in a RAM-like (random access memory) device nor in a reconfigurable system, such as a defect-tolerant communications and logic network. In addition, for rotaxane, an oxidation or reduction reaction occurs before the switch can be toggled. Thus, the reaction to toggle the switch requires an expenditure of a significant amount of energy. In addition, the large and complex nature of rotaxanes and related compounds potentially make the switching times of the molecules slow. The catenane-based switches have displayed small ON-to-OFF ratios and have also displayed slow switching times.